LU-7528 test: Deregister changelog client on test fail.

LU-7528 test: Deregister changelog client on test fail.

The tests which are related to changelog did not deregister
changelog when any failure was encountered, because of which
any changes afterward were also recorded leading to huge
test stdouts. I have added the functions changelog_cleanup
which will deregister the changelog client created by the
test before exiting. This function is to be used in place
of changelog deregister in any test that registers a changelog
client and a trap statement is included to execute this
function on EXIT.

Test-Parameters: trivial

Seagate-bug-id: MRP-3063
Signed-off-by: Kirtankumar Krishna Shetty <kirtan.shetty@seagate.com>
Change-Id: I7f26f266ba8bda294b75ff5619d95c26704fd83f
Reviewed-on: http://review.whamcloud.com/17506
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>